/*
 * Copyright 2002-2017 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.web.reactive.result.method.annotation;

import java.util.List;
import java.util.Map;

import org.springframework.beans.factory.config.ConfigurableBeanFactory;
import org.springframework.core.MethodParameter;
import org.springframework.core.ReactiveAdapterRegistry;
import org.springframework.core.convert.ConversionService;
import org.springframework.lang.Nullable;
import org.springframework.util.Assert;
import org.springframework.web.bind.annotation.RequestHeader;
import org.springframework.web.server.ServerWebExchange;
import org.springframework.web.server.ServerWebInputException;

/**
 * Resolves method arguments annotated with {@code @RequestHeader} except for
 * {@link Map} arguments. See {@link RequestHeaderMapMethodArgumentResolver} for
 * details on {@link Map} arguments annotated with {@code @RequestHeader}.
 *
 * <p>An {@code @RequestHeader} is a named value resolved from a request header.
 * It has a required flag and a default value to fall back on when the request
 * header does not exist.
 *
 * <p>A {@link ConversionService} is invoked to apply type conversion to resolved
 * request header values that don't yet match the method parameter type.
 *
 * @author Rossen Stoyanchev
 * @see RequestHeaderMapMethodArgumentResolver
 * @since 5.0
 */
public class RequestHeaderMethodArgumentResolver extends AbstractNamedValueSyncArgumentResolver {

    /**
     * @param factory a bean factory to use for resolving  ${...}
     * placeholder and #{...} SpEL expressions in default values;
     * or {@code null} if default values are not expected to have expressions
     * @param registry for checking reactive type wrappers
     */
    public RequestHeaderMethodArgumentResolver(@Nullable ConfigurableBeanFactory factory,
            ReactiveAdapterRegistry registry) {

        super(factory, registry);
    }


    @Override
    public boolean supportsParameter(MethodParameter param) {
        return checkAnnotatedParamNoReactiveWrapper(param, RequestHeader.class, this::singleParam);
    }

    private boolean singleParam(RequestHeader annotation, Class<?> type) {
        return !Map.class.isAssignableFrom(type);
    }

    @Override
    protected NamedValueInfo createNamedValueInfo(MethodParameter parameter) {
        RequestHeader ann = parameter.getParameterAnnotation(RequestHeader.class);
        Assert.state(ann != null, "No RequestHeader annotation");
        return new RequestHeaderNamedValueInfo(ann);
    }

    @Override
    protected Object resolveNamedValue(String name, MethodParameter parameter, ServerWebExchange exchange) {
        List<String> headerValues = exchange.getRequest().getHeaders().get(name);
        Object result = null;
        if (headerValues != null) {
            result = (headerValues.size() == 1 ? headerValues.get(0) : headerValues);
        }
        return result;
    }

    @Override
    protected void handleMissingValue(String name, MethodParameter parameter) {
        String type = parameter.getNestedParameterType().getSimpleName();
        throw new ServerWebInputException("Missing request header '" + name +
                "' for method parameter of type " + type);
    }


    private static class RequestHeaderNamedValueInfo extends NamedValueInfo {

        private RequestHeaderNamedValueInfo(RequestHeader annotation) {
            super(annotation.name(), annotation.required(), annotation.defaultValue());
        }
    }

}
